1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for chemical vapor deposition (CVD) on a substrate, and in particular, to a showerhead assembly made up of multiple plates fastened together for delivering multiple precursors therethrough without mixing prior to exiting the showerhead.
2. Description of the Related Art
Group III-V films are finding greater importance in the development and fabrication of a variety of semiconductor devices, such as short wavelength light emitting diodes (LED's), laser diodes (LD's), and electronic devices including high power, high frequency, high temperature transistors and integrated circuits. For example, short wavelength (e.g., blue/green to ultraviolet) LED's are fabricated using the Group III-nitride semiconducting material gallium nitride (GaN). It has been observed that short wavelength LED's fabricated using GaN can provide significantly greater efficiencies and longer operating lifetimes than short wavelength LED's fabricated using non-nitride semiconducting materials, such as Group II-VI materials.
One method that has been used for depositing Group III-nitrides, such as GaN, is metal organic chemical vapor deposition (MOCVD). This chemical vapor deposition method is generally performed in a reactor having a temperature controlled environment to assure the stability of a first precursor gas which contains at least one element from Group III, such as gallium (Ga). A second precursor gas, such as ammonia (NH3), provides the nitrogen needed to form a Group III-nitride. The two precursor gases are injected into a processing zone within the reactor where they mix and move towards a heated substrate in the processing zone. A carrier gas may be used to assist in the transport of the precursor gases towards the substrate. The precursors react at the surface of the heated substrate to form a Group III-nitride layer, such as GaN, on the substrate surface. The quality of the film depends in part upon deposition uniformity which, in turn, depends upon uniform mixing of the precursors across the substrate at a uniform temperature across the substrate.
Multiple substrates may be arranged on a substrate carrier and each substrate may have a diameter ranging from 50 mm to 100 mm or larger. The uniform mixing of precursors over larger substrates and/or more substrates and larger deposition areas is desirable in order to increase yield and throughput. These factors are important since they directly affect the cost to produce an electronic device and, thus, a device manufacturer's competitiveness in the marketplace.
Interaction of the precursor gases with the hot hardware components, which are often found in the processing zone of an LED or LD forming reactor, generally causes the precursor to break-down and deposit on these hot surfaces. Typically, the hot reactor surfaces are formed by radiation from the heat sources used to heat the substrates. The deposition of the precursor materials on the hot surfaces can be especially problematic when it occurs in or on the precursor distribution components, such as the gas distribution device. Deposition on the precursor distribution components affects the flow distribution uniformity over time. Therefore, the gas distribution device may be cooled during deposition processes, which reduces the likelihood that the MOCVD precursors, or HVPE precursors, are heated to a temperature that causes them to break down and affect the performance of the gas distribution device.
As the desired deposition areas increase, the size and complexity of conventional gas distribution devices that are configured to deliver multiple processing gases to the substrates increases, which results in significantly increased manufacturing and transportation costs. For example, in a multiple precursor gas distribution device, a plurality of manifolds and gas passages may be formed in a number of large plates that are then stacked and permanently attached to form the multiple precursor gas distribution device. As the gas distribution devices increase to cover deposition areas of 1 m2 and greater with the number of gas distribution passages exceeding 5000 in number, the complexity and cost of manufacturing these devices dramatically increases. Therefore, there is a need for an improved gas distribution device to provide improved uniformity in the film subsequently deposited over the larger substrates and larger deposition areas while reducing the complexity and manufacturing cost of the gas distribution device.